Flexible sheeting that is thermoformed is prominently used in applications where consumers are looking for comfort, luxury look and feel, or convenience. Applications are typically centralized in automotive door panel skins, instrument panel skins, and flooring where low-gloss is desired. For many years, flexible PVC was the dominant material used in thin gauge thermoforming, but with the change in automotive interior design came the need for alternate materials that could satisfy low temperature impact performance in seam-less airbag design and also have improved fogging resistance or reduced volatile organic components (VOCs). Flexible thermoplastic polyolefins (TPOs) address some of the short comings of flexible PVC because they don't use plasticizers that cause fogging issues, yet they still exhibit a broad temperature performance window (−40° C. to 120° C.).
However, a majority, if not all, of current flexible TPO sheeting that is used in sun-light exposed parts currently has urethane coatings applied to them to reduce the gloss, and to minimize low molecular weight or degradation components exudation to the surface which are known to increase tackiness and gloss over the vehicle life-time. High gloss is often equated to “cheap/plastic look and feel” whereas low gloss is an attribute that is commonly equated to luxury look and feel, approaching that of leather, and often brings a high value in use proposition. Additionally, glare off of high gloss surfaces may create unsafe driving conditions. Over the last decade, flexible TPOs have not demonstrated the ability to deliver low gloss after thermoforming or a dry feel after weathering—which is one of the main reasons that coatings are used. Coatings add significant costs to TPO sheeting and not all sheet producers have assets in place to use coatings.
TPO compositions for use in low gloss sheet that can maintain low gloss through extended weathering exposure have been developed. TPO blends of one or more ethylene/α-olefin elastomers and one or more polypropylenes to make fabricated articles or products, e.g., instrument panels and door panels, are known. See, for example, U.S. Pat. No. 6,372,847, US Publication No, 2007/0167575 and International Publication No. WO 00/26268. These blends and products demonstrate many desirable qualities, e.g., good to superior melt strength and processability, moldability, impact and mar resistance, modulus, elasticity, and the like. However, in some applications, the fabricated articles or products still exhibit too much gloss.
Various other methods exist for controlling gloss. One method incorporates a filler, e.g., talc, mica, etc., into the blend before thermoforming (typically, the more filler of uneven surface, the less gloss exhibited in a finished product). Other methods include the following: (1) control of the surface of the mold (the smoother the mold surface, the higher the gloss), (2) incorporation of pigment into the blend (different pigments absorb different light frequencies) and (3) elastomer selection (e.g., ethylene/α-olefin copolymer, EPDM, etc.) and blend ratios of “elastomer to crystalline or matrix polymer (e.g., polypropylene).”
While these various methods of controlling gloss are all effective to one degree or another, none are without problems or disadvantages. The use of fillers and/or pigments requires at least one additional blending step and increases the specific gravity of the blend. The addition of fillers and/or pigments may also require the use of other processing aids to facilitate dispersion, throughput and the like. This, in turn, increases the cost of the blend, both in terms of materials and processing costs. Treatment of the mold surface can be problematic, both in terms of effectiveness and cost, especially if the mold is used to prepare products of different gloss values (thus necessitating a separate mold for each gloss requirement). Varying the type and amount of elastomer in the blend is usually preferable to the use of fillers and pigments, but can have a material impact on certain properties of the final product, e.g., modulus, impact resistance, heat resistance, and other mechanical properties.
Thus, there is a need for polymer compositions in which the levels of the polymeric components can be varied to reduce gloss levels in the final products, without impairing rheological, thermal, and/or mechanical properties of the compositions or the final products.